Recently, as a result of rapid advancements in communication techniques, electric, radio, optical, and other signals are transmitted in compliance with various communication protocols (communication rules). In transmitting those signals, a conversion adapter for converting signals transmitted in compliance with one communication protocol to signals transmitted in compliance with another communication protocol may be used (for example, see Patent Literature 1). Patent Literature 1 describes, as such a conversion adapter, a packet node connecting a communication network to another communication network.